MOVIES : Voyage to the Next Dimension : With the visual effects process Introvision, film makers can transport actors to settings limited only by the imagination

Entrenched in the soft dirt of dense jungle outside Hanoi, a tank and anti-aircraft gun rake the sky with rounds of flak. A low-flying A-6 Intruder, red-ribboned with tracers, drops a bomb. Suddenly, a hot white flash bursts behind the anti-aircraft gun, hurling chunks of earth and jagged shards of metal outward.

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Two boys running for their lives along a towering wooden train trestle spanning a deep gorge. A locomotive barrels down on the boys, nipping at their heels, snorting angrily in fire-belly bursts of steam. The trestle is too long, the train too fast. The massive locomotive looms up behind them, about to crush the boys between the steel rails, when they reach the end of the trestle and tumble off the track to safety.

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A man strolling in a busy office, navigating his way through a corporate sea of blue blazers and wagging tongues as he talks to us. Without warning, all action in the room freezes into a still photo--except for the man, who continues wandering among the people and furniture, telling us about the advantages of a phone system. He finishes his pitch. The room unfreezes and the action resumes.

FADE OUT.

The three scenes above have one thing in common--they were all shot inside the same 100-square-foot area of a sound studio. A jungle scene in Paramount Pictures' war film, "Flight of the Intruder," the perilous train scene from Rob Reiner's "Stand by Me" and the Clio Award-winning commercial for AT&T were all accomplished with Introvision, a visual effects process that has been fooling movie and TV audiences for a decade.

The system can transport live-action actors to virtually any setting imaginable and allow them to step inside their surroundings. Actors move around within a three-dimensional, illusory landscape, stepping in front of, around and behind objects that are not really there.

"Basically, the technique lets you create a foreground and a middle ground in front of a background that you've already shot," said director John Milius, who directed the $30-million "Flight of the Intruder," which opens Friday. "You can shoot miniature explosions and things like that, and then put real people in front of the explosions."

Director Dick Lowry, whose TV movie "Miracle Landing" last year re-created the midair disaster that ripped the top off Aloha Airlines Flight 243, said: "We had airplane parts, luggage, heavy steel items and metal flying at passengers, and, in fact, they're weren't. But visually you look at it on film and you cannot tell."

Introvision is not in the business of producing mind-blowing, alien-zapping, phosphorescent special effects. Instead, the system relies on sleight of hand to deceptively fool audiences. "There's no such thing as reality in film," Introvision owner and president Tom Naud said. "Motion pictures are nothing but a succession of still pictures. Once you understand that, you can unlock all kinds of mysteries."

Shooting actors in front of a fake backdrop is nothing new. The earliest attempts used the famous "carousel," which allowed actors to ride dummy horses or cars while the countryside rolled along behind them. What audiences didn't see was the man just off-screen cranking the large cylindrical painted backdrop that revolved behind the actors. A more effective process was rear projection and front projection. For those, a previously filmed background scene was projected onto a screen and rephotographed with actors standing in front of it.

Introvision distinguishes itself by using a dual front screen projection system that not only places images behind, but in front of the subject as well, allowing the actors to walk around in a three-dimensional space. It was Introvision that shoved the little girl down the slippery glass atop a skyscraper in "Adventures in Babysitting," dropped Sylvester Stallone from the ceiling of a cave in Israel with a fireball bursting behind him in "Rambo III," and sent Weird Al Yankovic fleeing from a boulder in an Indiana Jones parody for the film "UHF."

"Introvision is best used for shots that would otherwise put the actors in a lot of jeopardy," said film director John Avildsen, who used the process to make Ralph Macchio appear to scale down a precarious cliff in "Karate Kid III." "I think they've built the best mousetrap. Imagination is the only limitation. I think they have their act down so you can do most anything a script calls for."

Naud claims he can shoot grand-scale scenes for far less money and in less than half the time required for the traditional method of constructing elaborate sets or traveling to exotic locales and mounting full-scale productions. Savings come from not having to build sets at all--a miniature model, a painting or even a still postcard-sized photograph can create a world that actors can step inside and inhabit.